Dielectric Relaxation Response Research Articles

Dielectric relaxation response of electrical insulating liquids under different natures of thermal stress

This study focuses on the dielectric relaxation response of insulating liquids based on mineral oil and synthetic ester in a thermal field.The research also offers the dielectric relaxation response of the magnetic nanofluid based on the investigated synthetic ester. The reason for investigating the synthetic ester-based nanofluid is that the temperature characteristics of the mineral oil-based magnetic nanofluid have already been investigated in several studies. Nanofluid based on synthetic ester is not sufficiently explored in this regard. The behavior of insulating liquids in the thermal field is divided into two parts. The first one points to the effect of temperature on the dielectric properties of the insulating liquids in the range from 293.15 K to 363.15 K. The insulating liquids show relaxation processes in the investigated frequency spectrum (1 mHz–3 kHz), which are dependent on temperature. The logarithm of the relaxation frequency decreases linearly with decreasing temperature according to Arrhenius' law. Mineral oil has the highest value of activation energy. In the second part, the results are focused on the influence of the rate of temperature increase on the dielectric parameters and moisture content of the investigated fluids. A slower increase in temperature causes an increase in polarization losses and a reduction in the distribution of relaxation times. In the case of base oils, also a reduction in activation energy. The change in the heating rate of the investigated liquids does not affect their moisture. Changes in dielectric parameters are not caused by changes in the moisture of insulating liquids, but by thermal aging.

Experimental study and DFT calculations of improved giant dielectric properties of Ni2+/Ta5+ co-doped TiO2 by engineering defects and internal interfaces

High-performance ceramics with chemical formula (Ni1/3Ta2/3)xTi1−xO2 with excellent dielectric properties are demonstrated. The dopants of Ni2+ and Ta5+ in TiO2 caused the formation of oxygen vacancies and free electrons. The (Ni1/3Ta2/3)xTi1−xO2 exhibited low loss tangent of 0.046 and a high dielectric permittivity of 3.5–4.5 × 104 with a very weak dependence on temperature (−60 to 200 °C). Broadband dielectric spectroscopy shows at least four dominant sources in the dielectric relaxation response in the temperature range of − 253–210 °C. DFT calculations indicate the formation of defect clusters, which are the largest contributors to the dielectric response, and these are found to be dominant even at temperatures down to − 253 °C. Both grain boundary and surface layer mechanisms in the ceramics contribute to the dielectric response at the relatively high temperatures. The sample–electrode contact effect associated with oxygen vacancy diffusion is dominant at high temperatures above 150 °C.

The abnormal multiple dielectric relaxation responses of Al3+ and Nb5+ co-doped rutile TiO2 ceramics

Al3+ and Nb5+ co-doped rutile TiO2 ceramic samples were prepared by solid state reaction. Raman spectra, element mapping and EDX confirmed that (Al + Nb) dissolved into grain. The samples showed colossal permittivity (ε′≈3.8 × 104) with low dielectric loss (under 0.08) over frequency (20 Hz–100 kHz) and temperature (80 K–240 K) ranges. Abnormal multiple dielectric relaxation properties were obtained around 5 K. Using universal relaxation law and thermal polaron hopping, we concluded that high dielectric constant of (Al1/2Nb1/2)0.05Ti0.95O2 was due to thermal activation of electrons in defect-dipoles, polaron hopping polarization and interfacial polarization. This investigation could increase our understanding models of multiple dielectric relaxation and inhomogeneous composition in co-doped rutile TiO2.

Defect driven d0 ferromagnetism and colossal dielectric behavior in Bi(Zn0.5Ti0.5)O3–PbTiO3 ceramics

We report room temperature ferromagnetism and colossal dielectric behavior in non-magnetic polycrystalline samples of x (BiZn0.5Ti0.5O3) – (1-x) (PbTiO3) with x = 0.25, 0.50. These samples are synthesized by mechanical alloying followed by heating the samples at elevated temperatures. Room temperature X-ray diffraction study reveals the formation of BZT-PT samples in perovskite phase and in the tetragonal system. The magnetic properties of these samples are studied by using SQUID. Intriguingly, exotic room temperature ferromagnetism has been observed in non-magnetic BZT-PT samples by vacuum annealing of the samples. In addition, a substantial high dielectric constant has also been observed in vacuum annealed samples. The unprecedented magnetic and dielectric behavior has been attributed to the formation of oxygen vacancies which is explained by further studying the magnetic and dielectric behavior in air annealed samples. Furthermore, the dielectric relaxation and frequency response of ac conductivity in BZT-PT samples found to follow universal dielectric relaxation and Johnscher's power law response, respectively. A detailed density functional calculations show that the exotic magnetism BZT-PT is mainly due to the partial occupancy of t2g and eg states of Ti ion by the delocalized electrons generated due to oxygen vacancy.

Segmental relaxation and partial crystallization of chain‐extended Poly(l‐lactic acid) reinforced with carboxylated carbon nanotube

ABSTRACTTemperature‐modulated differential scanning calorimetry (TMDSC) and broadband dielectric spectroscopy (BDS) were employed to study the glass transition, size of the cooperative rearranging regions (CRRs), crystallization kinetics, and dielectric relaxation response of nanocomposites constituted by chain‐extended poly(L‐lactide) (PLLA) and carboxylated carbon nanotubes (f‐CNTs). The CRR size and the number of relaxing structural units decreased in the presence of crystals during isothermal crystallization. All samples displayed both a primary (α) and secondary (β) relaxation in BDS spectra. The relaxation dynamics of PLLA chains was barely affected by the presence of the f‐CNT. Constrained polymer chains and thickness of interphase (t i) were measured using dielectric spectra in tan δ representation. t i values were found to be 46 and 24 nm for sample containing 0.2 and 0.5% weight fraction of f‐CNT, respectively. All samples underwent partial crystallization (with roughly 30% of final crystalline fraction) some 15 or 20° above their glass‐transition temperature (T g). Crystallization leads to a fragile‐to‐strong transition in the temperature dependence of the cooperative α relaxation and to the increased visibility of a Maxwell–Wagner–Sillars (MWS) interfacial relaxation, which appears to be present in all samples. The heterogeneity of the polymeric samples was quantified in terms of a new parameter, the heterogeneity index (H). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 222–233

Effect of Phospholipid Headgroup Charge on the Structure and Dynamics of Water at the Membrane Interface: A Terahertz Spectroscopic Study.

Biological membranes are highly organized supramolecular assemblies of lipids and proteins. The membrane interface separates the outer (bulk) aqueous phase from the hydrophobic membrane interior. In this work, we have explored the microstructure and collective dynamics of the membrane interfacial hydration shell in zwitterionic and negatively charged phospholipid membrane bilayers using terahertz time-domain spectroscopy. We show here that the relaxation time constants of the water hydrogen bond network exhibit a unique "rise and dip" pattern with increasing lipid concentration. More importantly, we observed a dependence of the critical lipid concentration corresponding to the inflection point on the charge of the lipid headgroup, thereby implicating membrane electrostatics as a major factor in the microstructure and dynamics of water at the membrane interface. These results constitute one of the first experimental evidences of the modulation of the dielectric relaxation response of membrane interfacial water by membrane lipid composition in a concentration-dependent manner. Lipid-stringent membrane hydration could be relevant in the broader context of lipid diversity observed in biological membranes and the role of negatively charged lipids in membrane protein structure and function.

Fundamental study on dielectric relaxation characteristics of cementitious materials

Dielectric frequency response measurement is utilized for a microstructure analyses of materials in various fields. The movements of the positive and the negative charges cause the response, which is so- called dielectric relaxation, and its measurement enables to clarify the interfacial composition of material. For example, the dielectric relaxation analysis of the human body cells is popular in the medical area. Gener- ally speaking, the indices of dielectric relaxation are capacitance, conductance, and susceptance. If the die- lectric relaxation measurement is applied to the concrete structure, there is a possibility to perform analyses of the concrete microstructures, because the interfacial compositions of aggregates, cement matrix, or pore solution dominate the dielectric relaxation responses of concrete theoretically. The correlations between concrete properties and dielectric relaxation responses are the significant information of concrete internal microstructures. This paper presents the results of the experimental examinations which were conducted to grasp the influence of the pore solution composition and the electrode interval on the dielectric relaxation properties. As a result, it became apparent that the behaviors of conductive electric charge, electric response charge, and displacement charge explain how sodium chloride and the distance between electrodes affected not only the magnitude of dielectric relaxation properties but also frequency spectrum.

New Routes to Functionalize Carbon Black for Polypropylene Nanocomposites.

Methods for chemical surface functionalization for carbon black (CB) nanoparticles were studied to produce (CB)/polypropylene (PP) nanocomposites with superior electrical and thermal properties. Nanoparticle dispersion is known to directly control the extent to which nanocomposites maximize the unique attributes of their nanoscale fillers. As a result, tailored nanoparticle surface chemistry is a widely utilized method to enhance the interfacial interactions between nanoparticles and polymer matrices, assisting improved filler dispersion. In this work, a rapid chemical functionalization approach using a number of diarylcarbene derivatives, followed by the azo-coupling of substituted diazonium salts, for the covalent introduction of selected functional groups to the CB surface, is reported. Characterization of the modified CB by XPS, TGA, CHN, and ATR-IR collectively confirmed surface functionalization, estimating surface grafting densities of the order of 10(13) and 10(14) molecules/cm(2). Nanocomposites, synthesized by solvent mixing PP with pristine and modified CB, demonstrated macroscopic property changes as a result of the nanoparticle surface functionalization. Pronounced improvements were observed for PP nanocomposites prepared with a dodecyl-terminated diaryl functionalized CB, in which TEM analysis established improved nanofiller dispersion owing to the enhanced CB-PP interfacial interactions in the nanocomposite. Observed dielectric relaxation responses at 20 wt % loading and a reduced percolation threshold realized conductivities of 1.19 × 10(-4) S cm(-1) at 10 wt %, compared to 2.62 × 10(-15) S cm(-1) for pristine CB/PP nanocomposites at the same filler loading. In addition, thermal properties signify an increase in the number of nucleation sites by the raised degree of crystallinity as well as increased melting and crystallization temperatures.

Dielectric response relaxation of PZT ceramics after electroding

ABSTRACTWe have studied the dielectric response dependence on frequency for piezoelectric ceramics based on lead zirconate - titanate (PZT) with three types of electrodes. There are found increase dielectric losses with the decrease of the frequency. Maximum value of tgδ depends on type of electrodes. Also for all samples observed relaxation of dielectric response on low frequency 10−2 – 103 Hz at time. But the total relaxation times are different. This behavior is explained by phenomena on the ceramics – electrode boundary.

Dielectric studies of al nanoparticle reinforced epoxy resin composites

Epoxy (EP) resin based nanocomposites with aluminum (Al) nanoparticles were prepared by solution method, with ultrasonic assisted dispersion followed by hot‐pressing methods. The dielectric permittivity, loss tangent, conductivity, and electric modulus of the nanocomposites were investigated by dielectric spectroscopy measurements in a wide frequency range from 1 to 107 Hz at temperatures from −20°C to 200°C. For all samples, the dielectric permittivity, dissipation factor, and electric conductivity increase with increasing temperature due to enhanced chain mobility above glass transition temperature (Tg). Broadband dielectric spectroscopy shows the multiple dielectric processes in the Al/epoxy nanocomposites corresponding to interfacial polarization (IP), α‐relaxation, and ionic conductivity, respectively. IP is detected at low frequencies and high temperatures. A primary α‐relaxation process is found at near Tg at the middle frequencies and the intermediate dipolar effect (IDE) is presented at high frequencies. The mechanisms responsible for dielectric relaxation, conductivity process, and electric modulus response have been discussed in detail. POLYM. COMPOS., 39:887–894, 2018. © 2016 Society of Plastics Engineers

Atypical Case of the Dielectric Relaxation Responses and its Fractional Kinetic Equation

Abstract We present a probabilistic model of the microscopic scenario of dielectric relaxation relating to the atypical case of two-power-law responses.The surveyed approach extends the cluster model concept used for the description of the typical, Havriliak-Negami (HN) law. Within the proposed framework, all empirical two-power-law relaxation patterns may be derived. Their relaxation functions are expressed in terms of the three-parameter Mittag-Leffler function, and the kinetic equation takes the pseudodifferential form generalizing the Riemann-Louiville fractional calculus. This provides a clue to explain the universality observed in relaxation phenomena.

The effect of monovalent cations on the collective dynamics of water and on a model protein

In this contribution we present experimental evidences of the ultrafast (sub-ps to ps) collective hydrogen bond dynamics of water in the extended hydration layers of alkali metal chlorides by using THz time domain spectroscopy (TTDS) in the terahertz frequency region (0.3–2.1THz; 10–70cm−1). The behaviour of the frequency dependent absorption coefficient (α), refractive index (n) and the dielectric relaxation response time (τ), obtained by fitting both real and imaginary parts of the permittivity (ε) using a triple Debye relaxation model are studied. The timescales obtained for bulk water are of the order of ~9ps, 200fs and 80fs. The relaxation time constant in the presence of the salt shows an accelerated reorientation dynamics of the water dipoles, which, in turn renders an indirect support for the ‘water structure breaking’ ability of monovalent ions, the effect being ion specific. We have also studied the effect of these ions on the secondary structure as well as hydration dynamics around a model protein bovine serum albumin (BSA). It is found that the structure and hydration of the protein as well as the salt hydration suffer negligible perturbation in the presence of the alkali metal chlorides.

Dynamics in Supercooled Secondary Amide Mixtures: Dielectric and Hydrogen Bond Specific Spectroscopies.

Alkylacetamide-based model peptides display an intense Debye-type dielectric relaxation. In order to explore the extent to which this feature has to be regarded analogous to that in other supramolecular liquids, notably the monohydroxy alcohols, we applied broadband dielectric, time-dependent solvation, and near-infrared spectroscopies as well as shear rheology and various nuclear magnetic resonance techniques to mixtures of N-methylacetamide (NMA) or N-ethylacetamide (NEA) with N-methylformamide. Compared in the modulus format, dielectric relaxation, solvation dynamics, and mechanical response indicate a common global and local dynamics. The present spin-relaxation measurements reflect motional processes which are significantly faster than the dominant Debye dielectric response, and a similar conclusion is drawn from measurements of the shear viscosity. The NH overtone stretching vibrations reveal a temperature-dependent hydrogen-bond equilibrium that changes its characteristics near temperatures of 325 K. Finally, dielectric low-temperature data recorded for (NEA)0.4(NMF)0.6 mixed with 2-picoline indicate the existence of a critical concentration akin to the situation in various monohydroxy alcohol mixtures.

Dielectric relaxation and magnetodielectric response in DyMn0.5Cr0.5O3

We investigate the structural, magnetic, and magnetodielectric properties of DyMn0.5Cr0.5O3. The sample can be indexed with an orthorhombic phase with B site disordered space group Pbnm. The valence state of both Mn and Cr ions are suggested to be +3 based on the results of x-ray photoelectron spectroscopy. Two thermally excited dielectric relaxation at temperatures TN2 < T< 300 K and large magnetodielectric effect (MDC = 20%–30%) due to the disordered arrangement of Mn3+/Cr3+ ions associated with electron hopping between them are observed. The absence of any noticeable magnetoresistance effect (MR < 0.5%) demonstrates that the observed magnetodielectric effect is an intrinsic behavior. These results suggest that DyMn0.5Cr0.5O3 is a magnetodielectric compound, whose dielectric properties are dependence of the applied magnetic field, which exhibits such effects near room temperature and holds great promise for future device applications.

Relaxation dynamics of surface-adsorbed water molecules in nanoporous silica probed by terahertz spectroscopy

Relaxation dynamics of an exclusively adsorbed water molecule in mesoporous silica MCM-41-S was studied by using terahertz spectroscopy. With the temperature controlled from 0 to 50 °C, we observed strongly frequency- and temperature-dependent dielectric relaxation responses, implying that, unlike ice, surface-adsorbed water molecules retained flourishing picosecond dynamics. Based on the Debye relaxation model, a relaxation time constant was found to increase from 1.77 to 4.83 ps when the water molecule was cooled from 50 to 0 °C. An activation energy of ∼15 kJ/mol, which was in close agreement with a hydrogen-bonding energy, was further extracted from the Arrhenius analysis. Combined with previous molecular dynamics simulations, our results indicate that the reorientation relaxation originated from the “flip-flop” rotation of a three hydrogen-bonded surface-adsorbed water molecule.

Dielectric relaxation dynamics of high-temperature piezoelectric polyimide copolymers

Polyimide copolymers have been prepared based on different diamines as comonomers: a diamine without CN groups and a novel synthesized diamine with two CN groups prepared by polycondensation reaction followed by thermal cyclodehydration. Dielectric spectroscopy measurements were performed, and the dielectric complex function, ac conductivity and electric modulus of the copolymers were investigated as a function of CN group content in the frequency range from 0.1 to 107 Hz at temperatures from 25 to 260 °C. For all samples and temperatures above 150 °C, the dielectric constant increases with increasing temperature due to increasing conductivity. The α-relaxation is just detected for the sample without CN groups, being this relaxation overlapped by the electrical conductivity contributions in the remaining samples. For the copolymer samples and the polymer with CN groups, an important Maxwell–Wagner–Sillars contribution is detected. The mechanisms responsible for the dielectric relaxation, conduction process and electric modulus response have been discussed as a function of the CN group content present in the samples.

Dielectric relaxation and electro-optic response in nano-ceria dispersed ferroelectric liquid crystal nanocomposites: effect of structural deformation and lattice straining

The current investigations deal with the effect of concentration of CeO2 nanoparticles (NPs) on physical properties of ferroelectric liquid crystal.

14.1: Low Temperature and High Frequency Effects on Blue Phase Liquid Crystals

AbstractWe report the low temperature and high frame rate operation limits of a polymer‐stabilized blue phase liquid crystal (BPLC). Debye relaxation sets another practical application limit even the temperature is still above melting point. Doping a diluter compound to the BPLC host greatly extends this low temperature operation range in terms of dielectric relaxation frequency and response time.

Characterization of a Sulfonated Polycarbonate Resistive Humidity Sensor

In this work; resistive moisture sensors were obtained by dip coating sulfonated polycarbonate (SPC) onto silver interdigitated electrodes. Commercial polycarbonate was sulfonated with acetyl sulphate at two different sulfonation degrees corresponding to 9.0 and 18.0 mole %. Impedance spectroscopy was used to investigate the humidity sensing properties at controlled relative humidity (RH%) environments generated from standard saline solutions in the range of 11–90 RH%. For the highest sulfonated sample; in the RH% range investigated (11 to 90%); the sensor impedance changed from 4.7 MΩ to 18 kΩ. Humidity sensors made from sulfonated polycarbonate showed exponential decay behavior of the impedance at constant frequency with the environmental relative humidity. Sample 9SPC presented dielectric relaxation response for environmental humidity between 58 and 90 RH% while sample 18SPC presented dielectric relaxation response for the entire measured range between 11 and 90 RH%. Sulfonated polycarbonate could be a promising material for the fabrication of simple and cheap humidity-sensing sensors for the assessment of relative humidity of the surrounding environment, as suggested by experimental results.

The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics

The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.